Fixing failing Behat scenarios in large suites

Warning: This blog post was written a long time ago and might be no longer relevant.
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In projects I currently work on I'm taking the BDD approach really seriously. In one of my Symfony2 projects I ended up with quite a lot of Behat features and scenarios which one day started failing on the integration server.

The problem was in MySQL returning "too many connections" response. To investigate it I logged into the MySQL console and checked running connections with show full processlist command.

Mysql process list

I noticed more and more connections being created and left in a sleep state while the scenarios are executed. At some point the number of connections reached the MySQL limit which was rejecting any new attempts to connect.

My first idea was to increase the limit (max_connections configuration option). Unfortunately it'd only hide the issue. In future it could come back as I'm constantly working on the project and still adding new scenarios.

Better solution would be to explicitly close the connections.

Doctrine2 ORM uses PDO and PDO connections are closed when last reference to the object is destroyed. Since Behat scenarios are all run in one process the destruction is postponed till all scenarios are executed.

Also, we have to remember that there are two types of connections:

  • connections created by Behat to build schema or load fixtures (Behat boots its own Symfony kernel)
  • connections created by the SymfonyDriver (client connections).

Note: Using other drivers (like Goutte) might limit total number of created connections as client would use a separate process. Unfortunately it's not enough in some cases (as Behat would still create its connections).

We might use AfterScenario hook to close all client connections (put it into subcontext):

/**
 * @param \Behat\Behat\Event\ScenarioEvent|\Behat\Behat\Event\OutlineExampleEvent $event
 *
 * @AfterScenario
 *
 * @return null
 */
public function closeDBALConnections($event)
{
    $this->getEntityManager()->clear();

    foreach ($this->getClientConnections() as $connection) {
        $connection->close();
    }
}

/**
 * @return array
 */
protected function getClientConnections()
{
    $driver = $this->getMainContext()->getSession()->getDriver();

    if ($driver instanceof \Behat\MinkBundle\Driver\SymfonyDriver) {
        return $driver->getClient()->getContainer()->get('doctrine')->getConnections();
    }

    return array();
}

I tried doing the same with Behat connections but they're not being closed. Luckily, the number of active connections decreased enough to make my scenarios pass again.

Note: If you're using CommonContexts (and you should!) than this fix is now included in the SymfonyDoctrineContext.

To improve the situation even better I limited amount of time MySQL waits before it closes connections automatically (wait_timeout configuration option). I didn't want to do it in the server configuration as I'd have to propagate it to all the machines scenarios are run on. Therefore I used PDO::MYSQL_ATTR_INIT_COMMAND attribute available in MySQL's PDO driver to set a session variable in the test environment.

In Symfony it can be easily done on a configuration level:

# app/config/config_test.yml
doctrine:
    dbal:
        dbname: testdb
        options:
            # 1002 == PDO::MYSQL_ATTR_INIT_COMMAND
            1002: 'SET SESSION wait_timeout=30;'

In combination with closing client connections this gave me the best results.

The only trick is to choose the timeout properly. We have to close the connections early enough to prevent exceeding the limit but late enough to make them available to the client for its whole execution time.

Jakub Zalas

Jakub Zalas

Agile PHP Developer, addicted to BDD and Symfony